A large amount of energy is required for the separation of carbon dioxide from emission gases of fossil-fueled power stations, for example combined cycle power stations (GUD) or coal-fired steam turbine power stations (DKW).
When a wet chemical absorption-desorption method is used for separation of carbon dioxide this energy must be applied in the form of thermal energy for heating the desorption process. Usually low-pressure steam from the steam circuit of the power station is used for this purpose.
To meet emission regulations GUD or DKW power stations without carbon dioxide separation must be retrofitted with a carbon dioxide separation device. These types of legacy stations generally do not yet have the appropriate precautions (Capture Readyness) for retrofitting of a carbon dioxide separation device.
Thus for example the machine house cannot be dimensioned sufficiently large for the additional piping for removal of the low-pressure steam, or the steam turbine or the power station process is not configured accordingly for the removal of low-pressure steam. With steam turbines with separate housings for the medium and low-pressure stage at least the removal of low-pressure steam at the overflow line is possible in a simple manner. On the other hand, for steam turbines with a single-housing medium and low-pressure stage, retrofitted units for removal of the necessarily large amount of steam are often not able to be realized, which is why the turbine has to be replaced in this case. In any event for the removal of low-pressure steam from the overflow line in the low-pressure section, the low-pressure section must be adapted to the modified suction capability (steam volume flow).
The removal of steam from other sources within the power station process is likewise not cost-effective or possible in a suitable manner Thus for example removal from an intermediate superheating line of the steam turbine without further measures leads to an unbalanced load of the boiler. The removal of high-quality steam for the carbon dioxide separation device must also be excluded without further measures, since this leads to unjustifiable energy losses.
A further problem which arises with the retrofitting of a carbon dioxide separation device is that on shutdown or failure of the carbon dioxide separation device the low-pressure temperature steam now not needed becomes superfluous. This excess steam cannot now simply be directed back into the steam turbine process since this is designed for operation with a carbon dioxide separation device, i.e. for a lower volume of steam.